(1) Field of the Invention
The present invention relates to an antenna device for receiving a radio wave transmitted from a communication satellite, converting the received radio wave into an electric signal, amplifying the signal, and outputting the amplified signal to a receiver, and a satellite communication reception system including an antenna device and a receiver.
(2) Description of the Related Art
In recent years, satellite communications have been finding widespread use as a new data transmission medium in international and domestic communication fields. A satellite communication system comprises a satellite orbiting around the earth and transmission and reception earth stations for accessing the satellite.
The reception earth station has an antenna device for receiving weak radiowaves transmitted from the satellite. The antenna device includes a converter assembly composed of an orthogonal mode transducer (OMT) and a low-noise block converter (LNB).
FIG. 9 of the accompanying drawings shows the converter assembly of a conventional antenna device. In FIG. 9, the converter assembly, generally denoted at 100m, serves to convert a radio wave received by an antenna (not shown) into an electric signal. The converter assembly 100m comprises an OMT 1 and an LNB 2m. The OMT 1 comprises a radio wave receiver 101 on a distal end thereof, a waveguide 102 contiguous to the radio wave receiver 101, and vertical and horizontal branching filters 103, 104 extending from the waveguide 102.
The LNB 2m is connected to the vertical and horizontal branching filters 103, 104 through a flange 105m having waveguide ports 106m, 107m (see FIG. 10 of the accompanying drawings) which are angularly displayed 90.degree. from each other. The vertical and horizontal branching filters 103, 104 also have respective waveguide ports (not shown in FIGS. 9 and 10) which are also angularly displayed 90.degree. from each other as with the waveguide ports 106m, 107m.
The LNB 2m comprises a vertical polarization LNB 50m and a horizontal polarization LNB 60m which are of an identical structure. The vertical polarization LNB 50m and the horizontal polarization LNB 60m are attached to the flange 105m such that they are angularly displayed 90.degree. from each other in registry with the waveguide ports 106m, 107m, respectively.
The vertical polarization LNB 50m is connected to the vertical branching filter 103 through the flange 105m, and the horizontal polarization LNB 60m is connected to the horizontal branching filter 104 through the flange 105m. The converter assembly 100m is supported by a support arm 111 extending from an end of the waveguide 102 which is joined to the radio wave receiver 101. The support arm 111 is fixed to an end 110m of an antenna.
A radio wave received by the antenna is supplied from the radio wave receiver 101 of the OMT 1, passes through the waveguide 102, and then is branched by the vertical and horizontal branching filters 103, 104 into vertically and horizontally polarized radiowaves, which are supplied to the respective LNBs 50m, 60m. The LNBs 50m, 60m amplify and convert the vertically and horizontally polarized radiowaves. For example, the LNBs 50m, 60m amplify and convert a radio wave in a 12 GHz band, which is transmitted from a broadcast satellite into a radio wave having a frequency in a 1 GHz band.
A satellite communication reception system employing the converter assembly 100m will be described below with reference to FIG. 11 of the accompanying drawings.
FIG. 11 shows an overall arrangement of a conventional satellite communication reception system. The illustrated satellite communication reception system is a CS broadcast reception system for receiving CS broadcast radiowaves from a satellite with television monitors. The satellite communication reception system has an antenna 110 for efficiently catching a weak 12 GHz radio wave transmitted from a satellite and supplying the received radio wave to the converter assembly 100m. The radio wave travels through the OMT 1 of the converter assembly 100m to the LNB 2m in which the vertically polarized radio wave V is amplified and converted into a signal having a frequency of 1 GHz by the vertical polarization LNB 50m and the horizontal polarized radio wave H is amplified and converted into a signal having a frequency of 1 GHz by the horizontal polarization LNB 60m. The frequency-converted signals are received by respective CS receivers (CS tuners) 71, 81, which output video and audio signals to television monitors 72, 82.
In the event of a failure of either one of the vertical polarization LNB 50m and horizontal polarization LNB 60m, a makeshift effort is made by removing the malfunctioning LNB 50m or 60m, turning the LNB 50m or 60m which is normal by 90.degree., and installing the turned LNB 50m or 60m.
For example, if the reception of a vertically polarized radio wave is indicated by the transmitting station, then when the vertical polarization LNB 50m fails to operate, four screws 108m (see FIG. 10) interconnecting the vertical polarization LNB 50m and the flange 105m are loosened, and the vertical polarization LNB 50m is detached from the flange 105m. At the same time, four screws 109m interconnecting the horizontal polarization LNB 60m which is not malfunctioning and the flange 105m are also loosened and removed from the flange 105m. Then, the horizontal polarization LNB 60m is angularly displaced 90.degree., and fastened by the four screws 108m to the flange 105m in the position from which the vertical polarization LNB 50m has been detached, i.e., over the waveguide port 106m. The waveguide port 107m which has been exposed is closed by a lid plate (not shown) using the four screws 109m to prevent from being made a hole in the horizontal polarization LNB60m of the frange 105m.
Therefore, when either one of the vertical polarization LNB 50m and the horizontal polarization LNB 60m suffers a failure, it has been tedious and timing-consuming to remove the faulty condition. If such a failure occurs in the middle of a radio wave reception, then the radio wave reception will be interrupted for a long period of time, resulting a possibility for the user to miss some important information which may be carried by the transmitted radio wave.
In the satellite communication reception system shown in FIG. 11, the LNBs 50m, 60m are supplied with electric energy from either the CS receivers 71, 81 or power supplies 73, 83, respectively. In such a power supply system, the CS receiver 71 or the power supply 73 for supplying electric energy to the LNB 50m is independent of the CS receiver 81 or the power supply 83 for supplying electric energy to the LNB 60m. Consequently, in the event that the CS receiver 71 or the power supply 73, or the CS receiver 81 or the power supply 83 fails to operate, the LNB 50m or 60m also fails to operate, resulting in the interruption of a radio wave reception as with the failure of the LNB 50m or 60m itself.